The present invention relates to a construction of a rotary machine such as a totally enclosed fan cooled rotary motor.
A conventional totally enclosed fan-cooled rotary motor has the following construction. As shown in FIG. 1, a stator comprising a stator core 2 and a stator coil 3 wound thereon is disposed within a stator frame 1 and is positioned between the inner periphery of the frame 1 and a rotor 5. The rotor 5 is disposed inward of the stator and is fixed to a rotary shaft 6. An end bracket 4 is fixed to one end of the stator frame 1. The rotary shaft 6 is rotatably supported by a bearing 7 which is in turn supported by the bracket 4. One end of the rotary shaft 6 extends through the end bracket 4, and a fan 8 is mounted to this shaft end. A fan cover 9 covering the fan 8 is fixed by bolts 11 to projection seats 10 provided on the end bracket 4.
The above-described construction entails the following problem. The fan cover 9 may resonate, generating large, unpleasant sound, when it is influenced by, e.g., incorrect balance of the rotor 5, electromagnetic vibration of the motor which includes high-frequency vibration when an inverter is driven, or gear meshing vibration of a geared motor.
In order to overcome the problem, the following proposals have hitherto been made:
(1) The adoption of a damping material as the material forming the fan cover;
(2) The adoption of a rubber vibration insulator, as shown in FIG. 2a or 2b. In the structure shown in FIG. 2a, a groove is formed on and around the side wall of a cylindrical rubber vibration insulator 12, while a hole is formed through the fan cover 9. The peripheral edge portion around the hole is fitted into the insulator groove. A bolt 11 is extended through a washer and the rubber vibration insulator 12, and is threaded into the projection seat 10, thereby fixing the fan cover 9 in place. In the structure shown in FIG. 2b, a rubber vibration insulator 12' is folded with a U-shaped section and has a protrusion which can be fit into a hole formed in the fan cover 9. A portion of the cover 9 is held between two layers of the rubber insulator 12'. A bolt 11 is threaded into the projection seat 10 in a similar manner, thereby fixing the fan cover 9 to the projection seats 10.
(3) The fan cover 9 is fixed to the projection seats 10 by means of plastic mounting pieces (see Japanese Patent Unexamined Publication No. 63-4156).
However, the above-described conventional vibration restraining means under Items (1) to (3) entail the following drawbacks:
The restraining means (1) is expensive because it employs as the damping material, a special material.
The restraining means (2) requires a long assembly time because the rubber vibration insulators must completely separate the fan cover from the projection seats. If the cover and the seats should brought into mutual contact through the bolts, the vibration restraining effect will be spoiled.
With the restraining means (3), the vibration insulating effect must be achieved at the sacrifice of strength.